Field of the Invention
The invention relates to a method for the cleaning of heat exchange tubes which are led through a tube plate of a heat exchanger, in particular of a heat exchanger of a nuclear plant, in which deposits in the heat exchange tubes are released and conveyed to a respective tube end. The invention also relates to a collecting device for the collection of deposits from heat exchange tubes led through a tube plate of a heat exchanger, in particular a heat exchanger of a nuclear plant.
When a heat exchanger is in operation, deposits may form in the heat exchange tubes. The deposits reduce the thermal conductivity of the heat exchange tubes and therefore the efficiency of the heat exchanger. In addition, the deposits make it difficult to check the heat exchange tubes for possible damage. That is because, for example, test heads are introduced into the heat exchange tubes for checking purposes. In that case, the measurement signals determined by the test heads may be influenced greatly by the deposits, so that it is only possible to obtain evidence as to the state of the heat exchange tubes to a limited extent.
It is necessary to check the heat exchange tubes for safety reasons, particularly in the case of a heat exchanger used in a nuclear plant. In a heat exchanger of that type, the deposits may be contaminated radioactively. Manual cleaning, in which the operating personnel would be directly exposed to the radioactive materials, is therefore usually disregarded. The aim is to carry out the cleaning of the heat exchange tubes as automatically as possible with the aid of manipulators.
Different methods may be employed in order to clean the heat exchange tubes. For example, they may be cleaned mechanically with the aid of a brush which is led through each heat exchange tube. The deposits may also be released and removed chemically or with the aid of abrasive blasting agents through the use of a blasting method.
A blasting method, in which the heat exchange tubes are first dried and subsequently treated with a compressed air/blasting agent mixture, is described in German Published, Non-Prosecuted Patent Application DE 195 46 788 A1, corresponding to U.S. Pat. No. 5,883,512. Through the use of that cleaning method, the heat exchange tubes are prepared for eddy current integrity testing, in order to improve fault detection during such a test.
Particularly in the case of a heat exchanger used in a nuclear plant, a situation must be avoided in which the released deposits and, possibly, abrasive blasting agents enter the heat exchanger and pass from there into other parts of the nuclear plant and influence its operation. It is therefore necessary for the released deposits and the abrasive blasting agents to be removed from the heat exchanger completely.